For what it’s worth, Adam Back has said there is solid legal precedent with TOR exit nodes and file sharing services that there is an established legal basis (in the U.S.) that would protect node runners of a public system in the event of CSAM on chain.

It is quite easily provable that a transaction and any data contained therein was submitted by a single entity and that all data hashed to the Bitcoin timechain is propagated to every node in perpetuity after submission and inclusion in a block. Demonstrably how the bitcoin protocol functions and easy to prove.